fix: improve code prompts to output only raw code

Add explicit instruction to all code generation prompts to return
only raw code without explanations, markdown, or code fences.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

lua/codetyper/utils.lua

@@ -17,7 +17,8 @@ function M.get_project_root()
     end
     found = vim.fn.finddir(marker, current .. ";")
     if found ~= "" then
-      return vim.fn.fnamemodify(found, ":p:h")
+      -- For directories, :p:h gives the dir itself, so we need :p:h:h to get parent
+      return vim.fn.fnamemodify(found, ":p:h:h")
     end
   end